Method of electrochemically fabricating multilayer structures having improved interlayer adhesion

ABSTRACT

Multi-layer microscale or mesoscale structures are fabricated with adhered layers (e.g. layers that are bonded together upon deposition of successive layers to previous layers) and are then subjected to a heat treatment operation that enhances the interlayer adhesion significantly. The heat treatment operation is believed to result in diffusion of material across the layer boundaries and associated enhancement in adhesion (i.e. diffusion bonding). Interlayer adhesion and maybe intra-layer cohesion may be enhanced by heat treating in the presence of a reducing atmosphere that may help remove weaker oxides from surfaces or even from internal portions of layers.

RELATED APPLICATIONS

This Application is a continuation-in-part of U.S. patent applicationSer. No. 10/434,289 filed on May 7, 2003, and claims benefit of U.S.Provisional Patent Application No. 60/533,946 filed on Dec. 31, 2003,U.S. Provisional Patent Application No. 60/506,103 filed on Sep. 24,2003, U.S. Provisional Patent Application No. 60/474,625 filed May 29,2003, and to U.S. Provisional Patent Application No. 60/468,741 filedMay 7, 2003; and the '289 application in turn claims benefit of U.S.Provisional Patent Application No. 60/379,129, filed on May 7, 2002.Each of these applications is hereby incorporated herein by reference asif set forth in full.

FIELD OF THE INVENTION

The embodiments of various aspects of the invention relate generally tothe formation of three-dimensional structures (e.g. meso-scale ormicroscale structures) using electrochemical fabrication methods whereinheat treatment is provided to improve interlayer adhesion.

BACKGROUND

A technique for forming three-dimensional structures (e.g. parts,components, devices, and the like) from a plurality of adhered layerswas invented by Adam L. Cohen and is known as ElectrochemicalFabrication. It is being commercially pursued by Microfabrica™ Inc.(formerly MEMGen® Corporation) of Burbank, Calif. under the name EFAB®.This technique was described in U.S. Pat. No. 6,027,630, issued on Feb.22, 2000. This electrochemical deposition technique allows the selectivedeposition of a material using a unique masking technique that involvesthe use of a mask that includes patterned conformable material on asupport structure that is independent of the substrate onto whichplating will occur. When desiring to perform an electrodeposition usingthe mask, the conformable portion of the mask is brought into contactwith a substrate while in the presence of a plating solution such thatthe contact of the conformable portion of the mask to the substrateinhibits deposition at selected locations. For convenience, these masksmight be generically called conformable contact masks; the maskingtechnique may be generically called a conformable contact mask platingprocess. More specifically, in the terminology of Microfabrica™ Inc.(formerly MEMGen® Corporation) of Burbank, Calif. such masks have cometo be known as INSTANT MASKS™ and the process known as INSTANT MASKINGor INSTANT MASK™ plating. Selective depositions using conformablecontact mask plating may be used to form single layers of material ormay be used to form multi-layer structures. The teachings of the '630patent are hereby incorporated herein by reference as if set forth infull herein. Since the filing of the patent application that led to theabove noted patent, various papers about conformable contact maskplating (i.e. INSTANT MASKING) and electrochemical fabrication have beenpublished:

(1) A. Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will,“EFAB: Batch production of functional, fully-dense metal parts withmicro-scale features”, Proc. 9th Solid Freeform Fabrication, TheUniversity of Texas at Austin, p161, August 1998.

(2) A. Cohen, G. Zhang, F. Tseng, F. Mansfeld, U. Frodis and P. Will,“EFAB: Rapid, Low-Cost Desktop Micromachining of High Aspect Ratio True3-D MEMS”, Proc. 12th IEEE Micro Electro Mechanical Systems Workshop,IEEE, p244, January 1999.

(3) A. Cohen, “3-D Micromachining by Electrochemical Fabrication”,Micromachine Devices, March 1999.

(4) G. Zhang, A. Cohen, U. Frodis, F. Tseng, F. Mansfeld, and P. Will,“EFAB: Rapid Desktop Manufacturing of True 3-D Microstructures”, Proc.2nd International Conference on Integrated MicroNanotechnology for SpaceApplications, The Aerospace Co., Apr. 1999.

(5) F. Tseng, U. Frodis, G. Zhang, A. Cohen, F. Mansfeld, and P. Will,“EFAB: High Aspect Ratio, Arbitrary 3-D Metal Microstructures using aLow-Cost Automated Batch Process”, 3rd International Workshop on HighAspect Ratio MicroStructure Technology (HARMST'99), June 1999.

(6) A. Cohen, U. Frodis, F. Tseng, G. Zhang, F. Mansfeld, and P. Will,“EFAB: Low-Cost, Automated Electrochemical Batch Fabrication ofArbitrary 3-D Microstructures”, Micromachining and MicrofabricationProcess Technology, SPIE 1999 Symposium on Micromachining andMicrofabrication, September 1999.

(7) F. Tseng, G. Zhang, U. Frodis, A. Cohen, F. Mansfeld, and P. Will,“EFAB: High Aspect Ratio, Arbitrary 3-D Metal Microstructures using aLow-Cost Automated Batch Process”, MEMS Symposium, ASME 1999International Mechanical Engineering Congress and Exposition, November,1999.

(8) A. Cohen, “Electrochemical Fabrication (EFABTM)”, Chapter 19 of TheMEMS Handbook, edited by Mohamed Gad-EI-Hak, CRC Press, 2002.

(9) “Microfabrication—Rapid Prototyping's Killer Application”, pages 1-5of the Rapid Prototyping Report, CAD/CAM Publishing, Inc., June 1999.

The disclosures of these nine publications are hereby incorporatedherein by reference as if set forth in full herein.

The electrochemical deposition process may be carried out in a number ofdifferent ways as set forth in the above patent and publications. In oneform, this process involves the execution of three separate operationsduring the formation of each layer of the structure that is to beformed:

1. Selectively depositing at least one material by electrodepositionupon one or more desired regions of a substrate.

2. Then, blanket depositing at least one additional material byelectrodeposition so that the additional deposit covers both the regionsthat were previously selectively deposited onto, and the regions of thesubstrate that did not receive any previously applied selectivedepositions.

3. Finally, planarizing the materials deposited during the first andsecond operations to produce a smoothed surface of a first layer ofdesired thickness having at least one region containing the at least onematerial and at least one region containing at least the one additionalmaterial.

After formation of the first layer, one or more additional layers may beformed adjacent to the immediately preceding layer and adhered to thesmoothed surface of that preceding layer. These additional layers areformed by repeating the first through third operations one or more timeswherein the formation of each subsequent layer treats the previouslyformed layers and the initial substrate as a new and thickeningsubstrate.

Once the formation of all layers has been completed, at least a portionof at least one of the materials deposited is generally removed by anetching process to expose or release the three-dimensional structurethat was intended to be formed.

The preferred method of performing the selective electrodepositioninvolved in the first operation is by conformable contact mask plating.In this type of plating, one or more conformable contact (CC) masks arefirst formed. The CC masks include a support structure onto which apatterned conformable dielectric material is adhered or formed. Theconformable material for each mask is shaped in accordance with aparticular cross-section of material to be plated. At least one CC maskis needed for each unique cross-sectional pattern that is to be plated.

The support for a CC mask is typically a plate-like structure formed ofa metal that is to be selectively electroplated and from which materialto be plated will be dissolved. In this typical approach, the supportwill act as an anode in an electroplating process. In an alternativeapproach, the support may instead be a porous or otherwise perforatedmaterial through which deposition material will pass during anelectroplating operation on its way from a distal anode to a depositionsurface. In either approach, it is possible for CC masks to share acommon support, i.e. the patterns of conformable dielectric material forplating multiple layers of material may be located in different areas ofa single support structure. When a single support structure containsmultiple plating patterns, the entire structure is referred to as the CCmask while the individual plating masks may be referred to as“submasks”. In the present application such a distinction will be madeonly when relevant to a specific point being made.

In preparation for performing the selective deposition of the firstoperation, the conformable portion of the CC mask is placed inregistration with and pressed against a selected portion of thesubstrate (or onto a previously formed layer or onto a previouslydeposited portion of a layer) on which deposition is to occur. Thepressing together of the CC mask and substrate occur in such a way thatall openings, in the conformable portions of the CC mask contain platingsolution. The conformable material of the CC mask that contacts thesubstrate acts as a barrier to electrodeposition while the openings inthe CC mask that are filled with electroplating solution act as pathwaysfor transferring material from an anode (e.g. the CC mask support) tothe non-contacted portions of the substrate (which act as a cathodeduring the plating operation) when an appropriate potential and/orcurrent are supplied.

An example of a CC mask and CC mask plating are shown in FIGS.1(a)-1(c). FIG. 1(a) shows a side view of a CC mask 8 consisting of aconformable or deformable (e.g. elastomeric) insulator 10 patterned onan anode 12. The anode has two functions. FIG. 1(a) also depicts asubstrate 6 separated from mask 8. One is as a supporting material forthe patterned insulator 10 to maintain its integrity and alignment sincethe pattern may be topologically complex (e.g., involving isolated“islands” of insulator material). The other function is as an anode forthe electroplating operation. CC mask plating selectively depositsmaterial 22 onto a substrate 6 by simply pressing the insulator againstthe substrate then electrodepositing material through apertures 26 a and26 b in the insulator as shown in FIG. 1(b). After deposition, the CCmask is separated, preferably non-destructively, from the substrate 6 asshown in FIG. 1(c). The CC mask plating process is distinct from a“through-mask” plating process in that in a through-mask plating processthe separation of the masking material from the substrate would occurdestructively. As with through-mask plating, CC mask plating depositsmaterial selectively and simultaneously over the entire layer. Theplated region may consist of one or more isolated plating regions wherethese isolated plating regions may belong to a single structure that isbeing formed or may belong to multiple structures that are being formedsimultaneously. In CC mask plating as individual masks are notintentionally destroyed in the removal process, they may be usable inmultiple plating operations.

Another example of a CC mask and CC mask plating is shown in FIGS.1(d)-1(f). FIG. 1(d) shows an anode 12′ separated from a mask 8′ thatincludes a patterned conformable material 10′ and a support structure20. FIG. 1(d) also depicts substrate 6 separated from the mask 8′. FIG.1(e) illustrates the mask 8′ being brought into contact with thesubstrate 6. FIG. 1(f) illustrates the deposit 22′ that results fromconducting a current from the anode 12′ to the substrate 6. FIG. 1(g)illustrates the deposit 22′ on substrate 6 after separation from mask8′. In this example, an appropriate electrolyte is located between thesubstrate 6 and the anode 12′ and a current of ions coming from one orboth of the solution and the anode are conducted through the opening inthe mask to the substrate where material is deposited. This type of maskmay be referred to as an anodeless INSTANT MASK™ (AIM) or as ananodeless conformable contact (ACC) mask.

Unlike through-mask plating, CC mask plating allows CC masks to beformed completely separate from the fabrication of the substrate onwhich plating is to occur (e.g. separate from a three-dimensional (3D)structure that is being formed). CC masks may be formed in a variety ofways, for example, a photolithographic process may be used. All maskscan be generated simultaneously, prior to structure fabrication ratherthan during it. This separation makes possible a simple, low-cost,automated, self-contained, and internally-clean “desktop factory” thatcan be installed almost anywhere to fabricate 3D structures, leaving anyrequired clean room processes, such as photolithography to be performedby service bureaus or the like.

An example of the electrochemical fabrication process discussed above isillustrated in FIGS. 2(a)-2(f). These figures show that the processinvolves deposition of a first material 2 which is a sacrificialmaterial and a second material 4 which is a structural material. The CCmask 8, in this example, includes a patterned conformable material (e.g.an elastomeric dielectric material) 10 and a support 12 which is madefrom deposition material 2. The conformal portion of the CC mask ispressed against substrate 6 with a plating solution 14 located withinthe openings 16 in the conformable material 10. An electric current,from power supply 18, is then passed through the plating solution 14 via(a) support 12 which doubles as an anode and (b) substrate 6 whichdoubles as a cathode. FIG. 2(a), illustrates that the passing of currentcauses material 2 within the plating solution and material 2 from theanode 12 to be selectively transferred to and plated on the cathode 6.After electroplating the first deposition material 2 onto the substrate6 using CC mask 8, the CC mask 8 is removed as shown in FIG. 2(b). FIG.2(c) depicts the second deposition material 4 as having beenblanket-deposited (i.e. non-selectively deposited) over the previouslydeposited first deposition material 2 as well as over the other portionsof the substrate 6. The blanket deposition occurs by electroplating froman anode (not shown), composed of the second material, through anappropriate plating solution (not shown), and to the cathode/substrate6. The entire two-material layer is then planarized to achieve precisethickness and flatness as shown in FIG. 2(d). After repetition of thisprocess for all layers, the multi-layer structure 20 formed of thesecond material 4 (i.e. structural material) is embedded in firstmaterial 2 (i.e. sacrificial material) as shown in FIG. 2(e). Theembedded structure is etched to yield the desired device, i.e. structure20, as shown in FIG. 2(f).

Various components of an exemplary manual electrochemical fabricationsystem 32 are shown in FIGS. 3(a)-3(c). The system 32 consists ofseveral subsystems 34, 36, 38, and 40. The substrate holding subsystem34 is depicted in the upper portions of each of FIGS. 3(a) to 3(c) andincludes several components: (1) a carrier 48, (2) a metal substrate 6onto which the layers are deposited, and (3) a linear slide 42 capableof moving the substrate 6 up and down relative to the carrier 48 inresponse to drive force from actuator 44. Subsystem 34 also includes anindicator 46 for measuring differences in vertical position of thesubstrate which may be used in setting or determining layer thicknessesand/or deposition thicknesses. The subsystem 34 further includes feet 68for carrier 48 which can be precisely mounted on subsystem 36.

The CC mask subsystem 36 shown in the lower portion of FIG. 3(a)includes several components: (1) a CC mask 8 that is actually made up ofa number of CC masks (i.e. submasks) that share a common support/anode12, (2) precision X-stage 54, (3) precision Y-stage 56, (4) frame 72 onwhich the feet 68 of subsystem 34 can mount, and (5) a tank 58 forcontaining the electrolyte 16. Subsystems 34 and 36 also includeappropriate electrical connections (not shown) for connecting to anappropriate power source for driving the CC masking process.

The blanket deposition subsystem 38 is shown in the lower portion ofFIG. 3(b) and includes several components: (1) an anode 62, (2) anelectrolyte tank 64 for holding plating solution 66, and (3) frame 74 onwhich the feet 68 of subsystem 34 may sit. Subsystem 38 also includesappropriate electrical connections (not shown) for connecting the anodeto an appropriate power supply for driving the blanket depositionprocess.

The planarization subsystem 40 is shown in the lower portion of FIG.3(c) and includes a lapping plate 52 and associated motion and controlsystems (not shown) for planarizing the depositions.

In addition to teaching the use of CC masks for electrodepositionpurposes, the '630 patent also teaches that the CC masks may be placedagainst a substrate with the polarity of the voltage reversed andmaterial may thereby be selectively removed from the substrate. Itindicates that such removal processes can be used to selectively etch,engrave, and polish a substrate, e.g., a plaque.

The '630 patent further indicates that the electroplating methods andarticles disclosed therein allow fabrication of devices from thin layersof materials such as, e.g., metals, polymers, ceramics, andsemiconductor materials. It further indicates that although theelectroplating embodiments described therein have been described withrespect to the use of two metals, a variety of materials, e.g.,polymers, ceramics and semiconductor materials, and any number of metalscan be deposited either by the electroplating methods therein, or inseparate processes that occur throughout the electroplating method. Itindicates that a thin plating base can be deposited, e.g., bysputtering, over a deposit that is insufficiently conductive (e.g., aninsulating layer) so as to enable subsequent electroplating. It alsoindicates that multiple support materials (i.e. sacrificial materials)can be included in the electroplated element allowing selective removalof the support materials.

Another method for forming microstructures from electroplated metals(i.e. using electrochemical fabrication techniques) is taught in U.S.Pat. No. 5,190,637 to Henry Guckel, entitled “Formation ofMicrostructures by Multiple Level Deep X-ray Lithography withSacrificial Metal layers”. This patent teaches the formation of metalstructure utilizing mask exposures. A first layer of a primary metal iselectroplated onto an exposed plating base to fill a void in aphotoresist, the photoresist is then removed and a secondary metal iselectroplated over the first layer and over the plating base. Theexposed surface of the secondary metal is then machined down to a heightwhich exposes the first metal to produce a flat uniform surfaceextending across the both the primary and secondary metals. Formation ofa second layer may then begin by applying a photoresist layer over thefirst layer and then repeating the process used to produce the firstlayer. The process is then repeated until the entire structure is formedand the secondary metal is removed by etching. The photoresist is formedover the plating base or previous layer by casting and the voids in thephotoresist are formed by exposure of the photoresist through apatterned mask via X-rays or UV radiation.

Another method of forming multilayer microstructures is taught in U.S.Pat. No. 6,332,568 to Todd Christenson, entitled “Wafer ScaleMicromachine Assembly Method”. This patent describes a method for fusingtogether, using diffusion bonding, micromachine subassemblies which areseparately fabricated. A first and second micromachine subassembly arefabricated on a first and second substrate, respectively. The substratesare positioned so that the upper surfaces of the two micromachinesubassemblies face each other and are aligned so that the desiredassembly results from their fusion. The upper surfaces are then broughtinto contact, and the assembly is subjected to conditions suited to thedesired diffusion bonding.

The formation of a micromechanical resonator was described by Wan-ThaiHsu, Seungbae Lee, and Clark T. C. Nguyen in a paper entitled “In SituLocalized Annealing for Contamination Resistance and Enhanced Stabilityin Nickel Micromechanical Resonators” published in “Digest of TechnicalPapers, 10th International Conference on Solid-State Sensors andActuators”, Sendai Japan, Jun. 7-10, 1999, pp. 932-935. This paperdescribes a technique in which a micromechanical resonator is operatedat large amplitudes while in situ localized annealing occurs attemperatures exceeding 880° C. Such annealing is shown to be aneffective method for both removal of surface contaminants and forpossible “redistribution” of the structural material towardssubstantially higher quality factor Q and greatly enhanced driftstability. The technique not only provides insight identifyingcontamination as a dominant mechanism for Q-degradation in nickel-platedmicromechanical resonators exposed to uncontrolled environments, butalso offers a convenient method for restoring a contaminated device toits original high-Q (Q=14,172) characteristics. This paper furtherdescribes a process for producing a nickel microresonator on whichtesting may be performed. The process begins with a silicon substrate onwhich 2 microns of oxide was grown. Next 300 angstroms of titanium and2700 angstroms of gold were evaporated and then patterned to forminterconnects. Next 1.8 microns of aluminum was evaporated and then viaswere patterned into the aluminum to expose the underlying gold. Next,nickel plating was used to create deposits that filled the vias and wastimed such that a planarized nickel aluminum surface was achieved in theregions of the vias. Next a 200 angstrom deposit of nickel wasevaporated over the entire surface. This evaporated deposit served as aseed layer and as the beginning of structural layer processing. Aphotoresist mold was then formed over the evaporated nickel and then 3microns of nickel was plated into mold. The mold and seed layer werethen removed and thereafter the aluminum was removed. The paper providesan SEM image of the resonator as well as a schematic of the electricalset up for testing.

A need exists in the art for improving adhesion between the layers of amultilayer structure when those layers are not formed separate from oneanother but are formed in intimate contact with one another and alreadyadhered to one another prior to heat treatment.

SUMMARY OF THE DISCLOSURE

It is an object of at least one aspect of the invention to provide anelectrochemical fabrication technique that yields improved properties offabricated structures.

It is an object of at least one aspect of the invention to provide anelectrochemical fabrication technique that yields improved interlayeradhesion.

It is an object of at least one aspect of the invention to provide aheat treated structure having significantly improved interlayer adhesionwhile not significantly reducing the yield strength of the intra-layermaterial.

It is an object of at least one aspect of the invention to reduce thepresence of metallic oxides that may be located along the interfacesbetween successively deposited layers or portions of layers.

It is an object of at least one aspect of the invention to provide aheat treated structure having improved properties where the structureremains protected by a sacrificial material until it is time for use.

Other objects and advantages of various aspects of the invention will beapparent to those of skill in the art upon review of the teachingsherein. The various aspects of the invention, set forth explicitlyherein or otherwise ascertained from the teachings herein, may addressany one of the above objects alone or in combination, or alternativelythey may not address any of the objects set forth above but insteadaddress some other object of the invention which may be ascertained fromthe teachings herein. It is not intended that all of these objects beaddressed by any single aspect of the invention even though that may bethe case with regard to some aspects.

In a first aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer of material to a previously formed layer and/or to asubstrate, wherein the layer includes a desired pattern of at least onematerial; and (b) repeating the forming and adhering operation of (a) atleast twice to build up a three-dimensional structure from a pluralityof adhered layers, wherein the desired patterning on at least two layersis different; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment; wherein thestructure includes at least one metal, and wherein formation of thedesired pattern for at least one layer includes use of an adhered mask.

In a second aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: forming a patterneddeposit of at least one first material on to a substrate or previouslydeposited material such that at least one void exists around or withinthe patterned deposit of the at least first material; depositing atleast one second material into at least a portion of the at least onevoid; (c) trimming the deposit of at least on of the at least one firstmaterial or the at least one second material to a desired level; (d)repeating the forming and adhering operations of (a)-(c) a plurality oftimes to build up a three-dimensional structure from a plurality ofadhered layers; (e) after formation of at least a plurality of layers,subjecting the multi-layer structure to heat treatment, wherein at leastone deposited material includes a metal, and wherein the forming of thepatterned deposit for at least one layer includes use of an adheredmask.

In a third aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate; and(b) repeating the forming and adhering operation of (a) at least once tobuild up a three-dimensional structure from a plurality of adheredlayers, wherein at least a plurality of the layers each include at leasttwo deposited materials; (c) after formation of at least a plurality oflayers and while at least two materials remain in contact adhered to oneanother, subjecting the multi-layer structure to a heat treatment;wherein the structure includes at least one metal.

In a fourth aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate; and(b) repeating the forming and adhering operation of (a) at least once tobuild up a three-dimensional structure from a plurality of adheredlayers, wherein the forming of at least a plurality of layers includesremoving at least some deposited material in a planarization operation;(c) after formation of at least a plurality of layers, subjecting themulti-layer structure to a heat treatment; wherein the structureincludes at least one metal, and wherein the forming and adhering of atleast one layer includes use of an adhered mask in the selectivepatterning of at least one material.

In a fifth aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers, wherein the desired patterning of at least one materialdeposited on a subsequent layer adheres directly to the desiredpatterning of at least one material deposited on a preceding layer; (c)after formation of at least a plurality of layers, subjecting themulti-layer structure to a heat treatment; wherein the structureincludes at least one metal, and wherein the forming and adhering of atleast one layer includes use of an adhered mask in the selectivepatterning of at least one material.

In a sixth aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein thestructure is heated in a manner such that any local temperaturevariations within the structure do not directly result from localizeddifferences in electrical conductivity of the structural material;wherein the structure includes at least one metal, and wherein theforming and adhering of at least one layer includes use of an adheredmask in the selective patterning of at least one material.

In a seventh aspect of the invention, a fabrication process for forminga multi-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment such thatsubstantially all portions of the structure are heated to asubstantially uniform temperature; wherein the structure includes atleast one metal.

In an eighth aspect of the invention, a fabrication process for forminga multi-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein amaximum temperature during heat treatment is less than arecrystallization temperature of at least one metal forming part of thestructure, and wherein the forming and adhering of at least one layerincludes use of an adhered mask in the selective patterning of at leastone material.

In a ninth aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers, wherein at least a plurality of the layers each includeat least one structural material and at least one sacrificial material;(c) separating the sacrificial material from the structure to releasethe structure; and (d) after formation of at least a plurality of layersbut prior to release, subjecting the multi-layer structure to a heattreatment; wherein the structure includes at least one metal, andwherein the forming and adhering of at least one layer includes use ofan adhered mask in the selective patterning of at least one material.

In a tenth aspect of the invention, a fabrication process for forming amulti-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers, wherein at least a plurality of the layers each includeat least one structural material and at least one sacrificial material,and wherein the desired patterning on at least two layers is different;(c) separating the sacrificial material from the structure to releasethe structure; and (d) after release, subjecting the multi-layerstructure to a heat treatment; wherein the structure includes at leastone metal, and wherein the forming and adhering of at least one layerincludes use of an adhered mask in the selective patterning of at leastone material

In an eleventh aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: (a) formingand adhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) subjecting the multi-layer structure to a heattreatment while the structure is located in a selected atmosphereincluding an inert gas, wherein the structure includes at least onemetal.

In a twelfth aspect of the invention, a fabrication process for forminga multi-layer three-dimensional structure, includes: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) subjecting the multi-layer structure to a heattreatment while the structure is located in a selected atmosphereincluding a reducing gas, wherein the structure includes at least onemetal.

In a thirteenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: (a) formingand adhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers, wherein at least a plurality of the layers each includeat least one structural material and at least one sacrificial material,and wherein the desired patterning on at least two layers is different;(c) separating the sacrificial material from the structure to releasethe structure; (d) after release, subjecting the multi-layer structureto a heat treatment; (e) after the heat treatment, applying a secondsacrificial material to the structure. wherein the structure includes atleast one metal.

In a fourteenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes:(a) formingand adhering a layer of material to a previously formed layer and/or toa substrate, wherein the layer includes a desired pattern of at leastone material; and (b) repeating the forming and adhering operation of(a) at least twice to build up a three-dimensional structure from aplurality of adhered layers; (c) after formation of at least a pluralityof layers, subjecting the multi-layer structure to a heat treatment; and(d) releasing the structure from the substrate, wherein the structureincludes at least one metal, and wherein the forming and adhering of atleast one layer includes use of an adhered mask in the selectivepatterning of at least one material.

In a fifteenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: Afabrication process for forming a multiple multi-layer three-dimensionalstructures, including: (a) forming and adhering a layer of material to apreviously formed layer and/or to a substrate, wherein the layerincludes a desired pattern of at least one material; and (b) repeatingthe forming and adhering operation of (a) at least twice to build up aplurality of three-dimensional structures from a plurality of adheredlayers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment; and (d) dicingthe plurality of structures from one another, wherein the structureincludes at least one metal.

In a sixteenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: (a) formingand adhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein amaximum effective temperature during heat treatment is less than arecrystallization temperature of at least one metal forming part of thestructure, and wherein the heat treatment is applied for a sufficienttime and at a sufficient temperature and in an environment that allowsinterlayer adhesion to be enhanced a substantial amount, and wherein theforming and adhering of at least one layer includes use of an adheredmask in the selective patterning of at least one material.

In a seventeenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: (a) formingand adhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein theheat treatment is applied to the structure for a temperature, a time,and in an environment such that a substantial increase in interlayeradhesion results without significantly reducing the yield strength ofthe intra-layer material, and wherein the forming and adhering of atleast one layer includes use of an adhered mask in the selectivepatterning of at least one material.

In an eighteenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: (a) formingand adhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein theheat treatment results in the formation of a structure which behavesmonolithically up to at least 50% of the yield strength of theintra-layer material, and wherein the forming and adhering of at leastone layer includes use of an adhered mask in the selective patterning ofat least one material.

In a nineteenth aspect of the invention, a fabrication process forforming a multi-layer three-dimensional structure, includes: (a) formingand adhering a layer to a previously formed layer and/or to a substrate,wherein the layer includes a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein theheat treatment results in the formation of a structure which is no morelikely to experience interlayer adhesion failure than intra-layercohesion failure when applied stress is at least 50% of the yieldstrength of the intra-layer material.

Further aspects of the invention will be understood by those of skill inthe art upon reviewing the teachings herein. Other aspects of theinvention may involve combinations of the above noted aspects of theinvention and/or addition of various features of one or moreembodiments. Other aspects of the invention may involve apparatus thatare configured to implement one or more of the above process aspects ofthe invention. These other aspects of the invention may provide variouscombinations of the aspects presented above as well as provide otherconfigurations, structures, functional relationships, and processes thathave not been specifically set forth above but which are ascertainablefrom the teachings herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-1(c) schematically depict side views of various stages of aCC mask plating process, while FIGS. 1(d)-(g) schematically depict aside views of various stages of a CC mask plating process using adifferent type of CC mask.

FIGS. 2(a)-2(f) schematically depict side views of various stages of anelectrochemical fabrication process as applied to the formation of aparticular structure where a sacrificial material is selectivelydeposited while a structural material is blanket deposited.

FIGS. 3(a)-3(c) schematically depict side views of various examplesubassemblies that may be used in manually implementing theelectrochemical fabrication method depicted in FIGS. 2(a)-2(f).

FIGS. 4(a)-4(i) schematically depict the formation of a first layer of astructure using adhered mask plating where the blanket deposition of asecond material overlays both the openings between deposition locationsof a first material and the first material itself.

FIG. 5 schematically depicts a heating system in which multiplestructures have been placed for heat treatment (e.g. diffusion bonding)in accordance with various embodiments of the invention.

FIG. 6 depicts a block diagram of a first embodiment of the inventionwhere a multilayer three-dimensional structure is formed and then heattreated such that, for example, interlayer adhesion is improved.

FIG. 7 depicts a block diagram of a second embodiment of the inventionwhere the formation of a multilayer three-dimensional structure includesan operation to planarize deposited layers of material and wherein thestructure is subjected to heat treatment after formation.

FIG. 8 depicts a block diagram of a third embodiment of the inventionwherein the formation of a multi-layer structure includes adheredsubsequently patterned layers of material directly to immediatelypreceding patterned layers of material and wherein the structure issubjected to heat treatment after formation.

FIG. 9 depicts a block diagram of a fourth embodiment of the inventionwherein the formation of a multi-layer structure includes the depositionof a plurality of materials during the formation of each layer andwherein the structure is subjected to heat treatment after formation.

FIG. 10 depicts a flowchart of a fifth embodiment of the invention whichmay be considered an expanded version of the fourth embodiment whereinone of the materials is a sacrificial material and may be removed eitherbefore or after heat treatment.

FIG. 11 depicts a block diagram of a sixth embodiment of the inventionwhere a structure is separated from a sacrificial material for heattreatment but is at least in part encapsulated with a sacrificialmaterial after heat treatment until it is ready to use or is put to useat which time the sacrificial material may be removed.

FIG. 12 depicts a flowchart of a seventh embodiment of the inventionwherein the structure may or may not be released from a substrate priorto heat treatment.

FIG. 13 depicts a flow chart of an eighth embodiment of the inventionwherein multiple multi-layer structures are formed which may bepartially or completed diced from one another prior to heat treatment.

FIG. 14 depicts a block diagram of a ninth embodiment of the inventionwhere the structure is heat treated, after formation, at a temperaturethat is less than a recrystallization temperature of at least one of thestructural materials from which the structure is formed.

FIG. 15 depicts a block diagram of a tenth embodiment of the inventionwhere the structure is heat treated after formation at a temperaturethat significantly enhances interlayer adhesion but does notsignificantly decrease the yield strength of the intra-layer material.

FIG. 16 depicts a block diagram of an eleventh embodiment of theinvention where the structure is heat treated at a temperature and timesuch that the multi-layer structure behaves monolithically up to atleast 50% of the yield strength of the intra-layer material forming thestructure.

FIG. 17 depicts a block diagram of an twelfth embodiment of theinvention where the structure is heat treated at a temperature and timesuch that the multi-layer structure behaves monolithically up to atleast 50% of the ultimate tensile strength of the intra-layer materialforming the structure.

FIG. 18 depicts a block diagram of a thirteenth embodiment of theinvention where the structure is heat treated in an atmosphere that isinert or that includes a reducing agent.

FIG. 19 depicts a block diagram of a fourteenth embodiment of theinvention where the structure is heat treated such that all portions ofthe structure reach a substantially uniform temperature.

FIG. 20 depicts a block diagram of a fifteenth embodiment of theinvention where the structure is heat treated such that localtemperature differences do not directly result from localizeddifferences in electrical conductivity (i.e. from ohmic heating fromcarrying an electric current).

FIG. 21 depicts a flowchart of a sixteenth embodiment where thestructure is partially formed, released from sacrificial material, thenheat treated, and then completed with or without refilling ofsacrificial material and with or without further heat treating.

FIGS. 22(a)-22(c) depict various views of the CAD design of a helicalspring-type contact element.

FIG. 22(d) depicts a number of helical spring-type contact elements ofFIGS. 22(a)-22(c) which are to be formed together in an array.

FIG. 22(e) depicts an SEM image of the microstructures of FIG. 22(d)created using an electrochemical fabrication process.

FIG. 23 depicts a substrate containing a plurality of devices similar tothose shown in FIG. 22(b) which have been heat treated and wherein oneof the devices has been subjected to a tensional force that hasstretched the structure beyond the elastic limits of the materialwherein the structure behaved monolithically (i.e. adhesion at the layerboundary did not fail).

DETAILED DESCRIPTION

FIGS. 1(a)-1(g), 2(a)-2(f), and 3(a)-3(c) illustrate various features ofone form of electrochemical fabrication that are known. Otherelectrochemical fabrication techniques are set forth in the '630 patentreferenced above (and in pending U.S. patent application Ser. No.09/493,496 which a divisional of the application that lead to the '630patent and is hereby incorporated herein by reference), in the variouspreviously incorporated publications, in various other patents andpatent applications incorporated herein by reference, still others maybe derived from combinations of various approaches described in thesepublications, patents, and applications, or are otherwise known orascertainable by those of skill in the art from the teachings set forthherein. All of these techniques may be combined with those of thevarious embodiments of various aspects of the invention explicitly setforth herein to yield enhanced embodiments. Still other embodiments maybe derived from combinations of the various embodiments explicitly setforth herein.

FIGS. 4(a)-4(i) illustrate various stages in the formation of a singlelayer of a multi-layer fabrication process where a second metal isdeposited on a first metal as well as in openings in the first metalwhere its deposition forms part of the layer. In FIG. 4(a), a side viewof a substrate 82 is shown, onto which patternable photoresist 84 iscast as shown in FIG. 4(b). In FIG. 4(c), a pattern of resist is shownthat results from the curing, exposing, and developing of the resist.The patterning of the photoresist 84 results in openings or apertures92(a)-92(c) extending from a surface 86 of the photoresist through thethickness of the photoresist to surface 88 of the substrate 82. In FIG.4(d), a metal 94 (e.g. nickel) is shown as having been electroplatedinto the openings 92(a)-92(c). In FIG. 4(e), the photoresist has beenremoved (i.e. chemically stripped) from the substrate to expose regionsof the substrate 82 which are not covered with the first metal 94. InFIG. 4(f), a second metal 96 (e.g., silver) is shown as having beenblanket electroplated over the entire exposed portions of the substrate82 (which is conductive) and over the first metal 94 (which is alsoconductive). FIG. 4(g) depicts the completed first layer of thestructure which has resulted from the planarization of the first andsecond metals down to a height that exposes the first metal and sets athickness for the first layer. In FIG. 4(h) the result of repeating theprocess steps shown in FIGS. 4(b)-4(g) several times to form amulti-layer structure are shown where each layer consists of twomaterials. For most applications, one of these materials is removed asshown in FIG. 4(i) to yield a desired 3-D structure 98 (e.g. componentor device).

The various embodiments, alternatives, and techniques disclosed hereinmay be used in combination with electrochemical fabrication techniquesthat use different types of patterning masks and masking techniques. Forexample, conformable contact masks and masking operations may be used,proximity masks and masking operations may be used (i.e. operations thatuse masks that at least partially selectively shield a substrate bytheir proximity to the substrate even if contact is not made),non-conformable masks and masking operations may be used (i.e. masks andoperations based on masks whose contact surfaces are not significantlyconformable), and adhered masks and masking operations may be used(masks and operations that use masks that are adhered to a substrateonto which selective deposition or etching is to occur as opposed toonly being contacted to it).

In still other embodiments, shielded conductive probes may be used as aform of direct writing of patterned deposits. An example of such anapproach is found in U.S. Pat. No. 5,641,391 to Hunter et al., entitled“Three Dimensional Microfabrication By Localized Electrodeposition andEtching” which is hereby incorporated herein by reference. In stillother embodiments multiple probes may be used simultaneously ormulti-cell masks may be used that allow selective cell-by-celldeposition or etching. Such masks and their use are described in U.S.patent application Ser. No. 10/677,498, filed on Oct. 1, 2003, andentitled “Selective Electrochemical Deposition Methods UsingPyrophosphate Copper Plating Baths Containing Ammonium Salts, CitrateSalts and/or Selenium Oxide”. This patent and application areincorporated herein by reference as if set forth in full herein.

Various embodiments of various aspects of the invention are directed toformation of three-dimensional structures from materials some of whichare to be electrodeposited or electroless deposited. Some of thesestructures may be formed from a plurality of layers of one or moredeposited materials (e.g. 3 or more layers, more preferably five or morelayers, and most preferably ten or more layers). In some embodimentsstructures having features positioned with micron level precision (e.g.less than 5 microns, preferably less than 1 micron and more preferablyless than about 0.5 microns) and minimum features size on the order ofmicrons or tens of microns (e.g. less than 20 microns, preferably lessthan 10 microns, and more preferably less than about 1 micron). In otherembodiments structures with less precise feature placement and/or largerminimum features may be formed. In still other embodiments, higherprecision and smaller minimum feature sizes may be desirable.

Various embodiments disclosed herein or portions of those embodimentsmay be supplemented by the above incorporated and known techniques byadding to them (for the formation of any given structure) processes thatinvolve the selective etching of deposited material and the filling ofcreated voids with additional materials. Various other embodiments ofvarious aspects of the invention, may depart from the selectivedeposition of materials entirely, and use blanket electrodepositionoperations to deposit materials and selective etching operations topattern those materials by creating voids that can be filled in usingblanket deposition operations. Various other embodiments may causedeposition of material to deviate from a strict layer-by-layer build upprocess. In a strict layer-by-layer build up process each layer iscomplete formed prior to beginning formation of a subsequent layer, e.g.an n^(th) layer is completely formed prior to beginning depositionoperations for forming a portion of an (n+1)^(th) layer. In thesealternative processes, formation of an (n+1)^(th) layer begins prior tocompleting the formation of an nth layer. All of these techniques areconsidered generalized layer-by-layer formation processes and they areused to produce multilayer structures where successively formed layersare adhered to previously formed adjacent layers. Such teachings arefurther described in U.S. patent application Ser. No. 10/434,519, filedMay 7, 2003 by Smalley, and entitled “Methods of and Apparatus forElectrochemically Fabricating Structures Via Interlaced Layers or ViaSelective Etching and Filling of Voids”. This patent application ishereby incorporated herein by reference as if set forth in full.

Other embodiments may use other forms of depositing material. Forexample, in some embodiments deposition of material may occur viachemical or physical vapor deposition (e.g. evaporation or sputtering),spreading, spraying, or the like. In some embodiments spray metalcoating processes may be used to obtain blanket or selectivedepositions. Spray metal coating techniques for forming threedimensional structures and particularly microstructures are described inU.S. patent application Ser. No. 10/697,597, filed on Oct. 29, 2003 byLockard et al., and entitled “EFAB Methods and Apparatus Including SprayMetal or Powder Coating Processes”. This patent application is herebyincorporated herein by reference. In some embodiments the heat treatingoperations may be used in conjunction with porous structural materialsto improve adhesion between the individual particles and/or to aid ininfiltrating a filler material into the pores of the structuralmaterial.

In still other embodiments heat treatment that improves interlayeradhesion may be combined with other post layer formation operations. Forexample packaging or hermetic sealing operations may be performed inconjunction with heat treatment operations. Hermetic sealing ofpackaging structures that surround components or other devices isdescribed in U.S. patent application Ser. No. 10/434,103, filed on May7, 2003, by Cohen et al, and entitled “Electrochemically FabricatedHermetically Sealed Microstructures and Methods of and Apparatus forProducing Such Structures”. This patent application is herebyincorporated herein by reference in its entirety.

FIG. 5 schematically depicts a heating system in which multiplestructures have been placed for heat treatment (e.g. diffusion bonding)according to various embodiments of the invention. The system contains aheating chamber 102 which includes resistive heating elements 104 and106 and temperature sensing device 108. The heating chamber may beselectively filled with any of a number of gases as indicated byelements 112, 114, and 116. Alternatively the chamber may be evacuatedusing a vacuum pump 118. Filling with gas may occur after evacuation orresult from a purging process that uses the gas via one or more outletslocated on the chamber. One or more structures (for example structures122, 124, or 126) may be placed in the chamber on support 128.Controller 132 may then be operated to evacuate the chamber or fill itwith an appropriate gas and then it may supply power to heating coils104 and 106 to raise the temperature within the chamber at a controlledrate and to a controlled final temperature after which the temperaturemay be lowered in a controlled manner or the system may simply be shutoff and the temperature allowed to lower as a result of heat dissipationfrom the chamber. Temperature sensor 108 may be used by the controllerin a feedback loop to ensure appropriate operation occurs. Thecontroller 132 may be a programmable device with an appropriate controlpanel and display panel. In other heating systems multiple temperaturesensors may be used and heat may be applied to the sample in other ways.For example, inductive coupling may be used to heat the samples burningof a fuel source may be used to supply heat via convection, conductionand/or radiative effects. Heating elements may be located below, beside,and/or above the structures to be heated. The chamber may also include afan or other elements for enhancing flow of gas within the chamber. Insome embodiments direct application of current applied to the sample orsamples may be used. This latter approach would seem particularly viablewhen the structure remains embedded in a conductive sacrificial materialbut it may also have application when structures are released and of adesign that would allow reasonably uniform current flow through allportions of the structure or where heat conduction via the structureitself may allow reasonable heat transfer and temperatures to beobtained.

FIG. 6 depicts a block diagram of a first embodiment of the inventionwhere a multilayer three-dimensional structure is formed and then heattreated such that, for example, interlayer adhesion is improved. Element152 of FIG. 6 calls for the formation of a multi-layer structure from aplurality of adhered layers. This formation process may involve one ofthe electrochemical fabrication processes discussed above, one of thefabrication processes incorporated herein by reference or some otherfabrication process that results in layers being formed on previouslyformed layers and adhered thereto. After formation of the structure theprocess moves forward to element 154 which calls for the supplying of aheat treatment to the structure such that interlayer adhesion, forexample, is enhanced. The heat treatment may be applied by a heatingsystem such as that illustrated in FIG. 5, or it may be applied in adifferent manner. The heat treatment is applied at a temperature and fora time that results in a desired increase in interlayer adhesion.

FIG. 7 depicts a block diagram of a second embodiment of the inventionwhere the formation of a multilayer three-dimensional structure includesan operation to planarize deposited layers of material and wherein thestructure is subjected to heat treatment after formation. Element 162 ofFIG. 7 calls for the formation of a three-dimensional structure whichincludes a plurality of adhered layers. The formation process willinclude the depositing of at least one material onto a substrate orpreviously formed layer such that at least a portion of the layer isformed. Then at least a portion of the deposited material is removed toobtain a planarized surface that may form an outward facing portion ofthe structure or alternatively it may form a surface onto whichadditional material may be adhered. Planarization may occur for exampleby lapping, polishing, chemical mechanical polishing, milling, diamondfly cutting, or the like. After the depositing and removing of materialto form a first layer or portion of a layer the depositing and removingsteps are repeated to form additional layers of the structure which areadhered together. After the formation of the structure is complete, theprocess moves forward to element 164 which calls for the heat treatingof the structure such that interlayer adhesion is enhanced.

FIG. 8 depicts a block diagram of a third embodiment of the inventionwherein the formation of a multi-layer structure includes subsequentlypatterned layers of material that are adhered directly to immediatelypreceding patterned layers of material and wherein the structure issubjected to heat treatment after formation. Element 172 of FIG. 8 callsfor the formation of a three-dimensional structure from a plurality ofadhered layers. The first operation involves the forming of a firstlayer from a deposit of at least one material where the material has apatterned configuration. The material may be deposited in a patternedmanner or it may be deposited in a blanket fashion where patterningoccurs after deposition. The formation of the first layer may includethe deposition of a second material or further materials, it may alsoinclude removal operations for the purpose of patterning or the purposeof planarization, and/or it may also include other operations such ascleaning operations, activation operations, process monitoringoperations, and the like. After the first layer is formed, a secondlayer is formed from the deposit of at least one material which has apatterned configuration. The patterned material deposited to form thesecond layer adheres, at least in part, directly to the patternedconfiguration of material forming the first layer. In other words, thereis no unpatterned intervening material that separates the first andsecond layers. In the formation of the structure a third operationinvolves the repeating the second operation as necessary to build up thestructure from the plurality of layers. During the repetition “second”is replaced by “n^(th)” and “first” is replaced by “(n−1)^(th)” where nis increment from 3 to N, where N is the number of the last layer to beformed. After formation of the structure is complete, the process movesforward to element 174 which calls for a heat treatment of the structuresuch that interlayer adhesion is enhanced.

FIG. 9 depicts a block diagram of a fourth embodiment of the inventionwherein the formation of a multi-layer structure includes the depositionof a plurality of materials during the formation of each layer andwherein the structure is subjected to heat treatment after formation.Element 182 calls for the formation of a multi-layer structure where thelayers are adhered to adjacent layers and wherein each layer includes atleast two deposited materials. Each of the materials may be structuralmaterial or alternatively at least one of the materials may be astructural material and at least one of the other materials may be asacrificial material. After the structure is formed the process movesforward to element 184 which calls for heat treating the structure suchthat interlayer adhesion is enhanced.

FIG. 10 depicts a flowchart of a fifth embodiment of the invention whichmay be considered an expanded version of the fourth embodiment where oneof the materials is a sacrificial material and may be removed eitherbefore or after heat treatment. The process of FIG. 10 begins withelement 192 which calls for the formation of a multi-layerthree-dimensional structure wherein adjacent layers are adhered to oneanother and where the structure includes at least one structuralmaterial and where at least one or more layers includes a sacrificialmaterial.

After the structure is formed, the process moves forward to element 194which makes an inquiry as to whether the sacrificial material is to bereleased from the structural material prior to heat treatment. If theanswer is “yes”, the process moves forward to element 196 which callsfor the release of the structure from the sacrificial material, forexample, via a chemical etching operation or the like. After which theprocess moves forward to element 200 which calls for heat treating thestructure such that interlayer adhesion is enhanced. If the answer tothe inquiry of element 194 is “no”, the process moves forward to element200 which calls for the heat treating of the structure such thatinterlayer adhesion is enhanced and thereafter the process moves forwardto element 202 which calls for the release of the structure from thesacrificial material. In some embodiments, it may be desirable torelease the structure from the sacrificial material prior to heattreating as the presence of the sacrificial material during heattreating may cause undesired alloying between a sacrificial material anda structural material or it may cause creation of undesiredinter-metallic compounds at the interface between the two materials.However, in other embodiments alloying and/or formation ofinter-metallic compounds may give desirable benefits. It may also bedesirable to cause the release prior to heat treatment since somestructural materials and sacrificial materials may have significantlydifferent coefficients of thermal expansion that could result inundesirable stresses being introduced into the structure during heattreating if the sacrificial material were present and if the heattreating temperature is high. In other embodiments it may be desirableto have the sacrificial material present at the time of heat treatmentof the structure, as the sacrificial material may form a mold that willhelp hold the structural material in its proper position duringtreatment.

FIG. 11 depicts a block diagram of a sixth embodiment of the inventionwhere a structure is separated from a sacrificial material before heattreatment but is at least in part encapsulated with a sacrificialmaterial after heat treatment until it is ready to use or is put to useat which time the sacrificial material may be removed. The process ofFIG. 11 begins with element 212 which calls for the formation of amulti-layer 3-dimensional structure where adjacent layers are adhered toone another. After the structure is formed, the process moves forward toelement 214 which calls for the release of the structure from at leastone sacrificial material. Thereafter the process moves forward toelement 216 which calls for the heat treating of the structure such thatinterlayer adhesion is enhanced. After heat treatment is completed theprocess moves forward to element 218 which calls for the applying of asacrificial material to the structure. This sacrificial material may bethe same as a sacrificial material used during the formation of thestructure, or it may be a different sacrificial material. For example,if the structural material is nickel, this sacrificial material may becopper. Alternatively it may be a photoresist material, a photopolymer,or some other material that may be applied to the structure in a liquidstate and then separated form the structure via chemical dissolution,melting, or the like. This applied sacrificial material may be useful inprotecting a delicate microstructure during a handling, shipping,mounting or during other processes to which the fragile structure may besubject. After the sacrificial material is applied the process movesforward to element 220 which calls for the mounting or otherwiselocating of the structure into a working position after which theprocess moves forward to element 222 which calls for the release of thestructure from the applied sacrificial material.

In some alternative embodiments the sacrificial material that is appliedafter heat treatment may remain in place during use of themicrostructure. For example such retention of the sacrificial materialmay be useful in an RF application where the sacrificial material may bea dielectric that helps support portions of coaxial structures and thelike. In other embodiments, more than one sacrificial material may beused during formation of the structure, at least one of the materialsmay be removed prior to heat treatment and at least one of the materialsmay remain during heat treatment, a portion of the remaining sacrificialmaterial may interact with the structural material during heat treatmentfor a beneficial purpose, and then after heat treatment at least aportion of this retained sacrificial material may be removed.Alternatively, the sacrificial material may be removed prior to heattreatment and another material added prior to heat treatment, heattreatment may occur with this extra-material in place, and then afterheat treatment the added material may be retained in whole or in part,or it may be removed in its entirety.

FIG. 12 depicts a flowchart of a seventh embodiment of the inventionwherein the structure may or may not be released from a substrate priorto heat treatment. In this embodiment it is recognized that it may bedesirable to release a structure from its substrate prior to performinga heat treatment operation. This may be desirable, for example, when thestructure is formed from a material which has a significantly differentcoefficient of thermal expansion from that of the substrate material.After heat treatment the structure could then be attached to a differentsubstrate or even potentially reattached to the initial substrate.

The process of this embodiment begins with element 232 which calls forthe formation of a multi-layer three-dimensional structure that haslayers adhered to one another. After formation of the structure theprocess moves forward to element 234 which inquires as to whether thestructure should be released from the substrate prior to heat treatment.If the answer is “yes”, the process moves forward to element 236 whichcalls for the release of the structure from the substrate. This releasemay occur, for example, via a meltable or dissolvable release layer thatis located between the substrate and the structure. Alternatively, itmay occur by machining away the substrate and/or etching and/orplanarizing away the substrate or a remaining portion of the substrate.After release of the structure from the substrate, the process movesforward to element 238 which calls for the heat treating of thestructure such that interlayer adhesion is enhanced. If the inquiry inelement 234 produced a negative response, the process would simply moveforward from element 234 to the heat treating operation of element 238.

FIG. 13 depicts a flowchart of an eighth embodiment of the inventionwherein multiple multi-layer structures are formed which may bepartially or completed diced from one another prior to heat treatment.The process of this embodiment begins with element 242 which calls forthe formation of multiple multi-layer structures. After formation of themulti-layer structures, the process moves forward to element 244 whichinquires as to whether partial or complete dicing of individualstructures should occur prior to heat treatment. In some circumstancesit may be desirable to partially or completely cut through sacrificialmaterial that may be located between adjacent die (i.e. individualstructures or sets of structures) prior to heat treatment so that stressbuild ups that might result from differentials in coefficients ofthermal expansion cannot propagate from relatively small individual dieregions across die boundaries to distal regions where they may reachmagnitudes that are capable of causing undesired distortions,delaminations, and the like.

If inquiry 244 produces a “yes” response, the process moves forward toelement 246 which calls for the dicing of the multiple structures.Thereafter the process moves forward to block 248 which calls for theheat treatment of the structures such that interlayer adhesion isenhanced. After the operation of element 248, the process may moveforward to element 252 which will be discussed shortly.

If inquiry 244 produces a “no” response, the process moves forward toelement 250 which calls for the heat treating of the structures suchthat interlayer adhesion is enhanced and thereafter the process movesforward to element 252 which calls for the dicing of the structures. Asnoted above, from element 248 the process may also move forward toelement 252 if dicing of element 246 was incomplete and if asupplemental dicing is beneficial to complete the separation process.

FIG. 14 depicts a block diagram of a ninth embodiment of the inventionwhere the structure is heat treated, after formation, at a temperaturethat is less than a recrystallization temperature of at least one of thestructural materials from which the structure is formed. The process forthis embodiment starts with element 262 which calls for the formation ofa multi-layer structure where adjacent layers are adhered to each other.After formation of the structure, the process moves forward to element264 which calls for heat treating the structure using a temperature thatis below the re-crystallization temperature of the structural materialbut is also sufficiently high and applied for a sufficient time suchthat enhanced interlayer adhesion results.

This embodiment can be illustrated with some experimental results. Inone set of experiments, adhesion tests were performed onelectrodeposited samples of nickel that were formed on a nickelsubstrate. Adhesion tests were also performed on similarly preparedsamples that underwent a heat treatment at about 450° C. for 5 to 9hours. Prior to performing the electroplating of the nickel, for allsamples, the surface of the nickel substrate was treated using anactivator known as C-12 Activator from Puma Chemical of Warne, N. C. Theactivation process followed the recommendations of the manufacturer. Thethree samples that did not undergo heat treatment showed adhesionfailures at about 44, 53, and 68 MPa. Three samples that underwent heattreatment showed adhesion failures at about 153, 215, and 280 MPa. Inother words, in this experiment, adhesion improved by a factor of about2.2 to a factor of about 6.4 with the average being about a factor of4.0.

In another experiment, numerous helical structures like those shown inFIG. 22(a)-22(e) were formed. FIGS. 22(a)-22(c) depict various views ofthe CAD design of a helical spring-type contact element. In this designthe thickness of each layer is 8 microns, the width of which helicalelement is 80 microns, the diameter of the overall helical element(excluding the base element) is 200 microns, and the overall height is160 microns. FIG. 22(d) depicts a number of helical spring-type contactelements of FIGS. 22(a)-22(c) which are to be formed together in anarray. FIG. 22(e) depicts an SEM image of the microstructures of FIG.22(d) created using an electrochemical fabrication process.

Some elements of an array like that of FIG. 22(e) were subjected to atensile pulling test to determine the viability of interlayer adhesion.Some samples that were pulled underwent a heat treatment while othersdid not. Four of the un-heat treated samples (each initially 160 micronsin height were pulled and each experienced interlayer adhesion failureat between 100 and 300 microns of extension. Heat treated samples thatwere pulled and were extended to a height of more than 2 millimeters andno delamination was observed. The heat treatment for these samplesincluded raising the samples to a temperature of 500° C. at a rate ofless than or equal to about 3° C. per minute and then holding the 500°C. temperature for 15 minutes and then cooling down the samples at arate of less than or equal to about 10° C. per minute. This heattreating process was performed with the structure in a forming gas whichincluded about 5% H2 and about 95% N2.

FIG. 23 illustrates numerous un-pulled heat treated structures such asstructures 372 and 374 along with one pulled structure 376 whichillustrates that the structure was pulled beyond the elastic limit ofthe material (i.e. into the plastic deformation region) and that theadhesion strength was greater than the yield strength of the structure(i.e. the stress and associated strain at which elastic deformationgives way to plastic deformation). Not only did these heat treatedsamples yield a significant improvement in interlayer adhesion, it isalso believed that a significant decrease in interlayer electricalresistance occurred. In these experiments, heat treatment of the sampleswas performed after release of the nickel structures from a coppersacrificial material.

It is believed that a dwell temperature (Td), i.e. a maximum temperatureof heating, of between 250° C. and 350° C. could be used to achievesignificant improvements in interlayer adhesion particularly if thedwell time is appropriately increased. It is also believed that heattreating at somewhat lower temperatures, e.g. 150° C. to 200° C. mayalso produce useful results. However, when working with nickelstructures it is believed a dwell temperature in the range of 350° C. to550° C., or somewhat higher, would allow a more timely obtainment ofdesired improvement in interlayer adhesion. It is believed that in someembodiments the dwell time (i.e. a time at the maximum temperature) ofless than 5 minutes could be used to achieve acceptable results. Whilein other embodiments a dwell time in the range of 5 minutes to 60minutes or even longer may be necessary or preferable. Lower dwelltemperatures and longer dwell times may be particularly beneficial whena portion of the structure or the substrate on which it is attached issusceptible to heat damage. It is believed that those of skill in theart can perform experiments to determine acceptable dwell temperaturesand dwell times as well as determining reasonable heating and coolingrates. For example, heating rates in some embodiments may be set in therange of 3° C. to 10C per minute or even higher.

Though in the present embodiment the maximum heat treating temperature(i.e. dwell temperature) is intended to be below the re-crystallizationtemperature of the structural material, it is believed that in someembodiments heat treating temperatures may exceed the re-crystallizationtemperatures.

For example, in some embodiments a preferred structural material mightbe nickel whereas in other embodiments preferred structural materialmight be copper. As nickel has a melting temperature of about 1455° C.and as the re-crystallization temperature of nickel is believed to beabout ½ of the absolute melting temperature (i.e. about 590° C.) it ispreferred to keep the heat treatment temperature below this 590° C.level. As the melting temperature of copper is about 1083° C. and as itis believed that the re-crystallization temperature of copper is about ⅓of the absolute melting temperature (i.e. about 200° C.) preferred heattreating operations for copper structures may use maximum temperaturesbelow this 200° C. value. In other embodiments, however, where otherstructural materials are used, or where nickel or copper alloys (e.g.nickel phosphor or nickel cobalt), or nickel or copper with differentlevels of impurities are used, different re-crystallization temperaturesmay exist and thus different maximum preferred heat treatmenttemperatures may exist. It is also understood that different depositionprocesses and/or metal working processes may yield differentrecrystallization temperatures for a given material and as such,different preferred ranges of heat treating temperatures may exist.

In applications where the structures, or components, formed are desiredto be harder and less ductile, then heat treating below there-crystallization temperature is preferred. However, in otherapplications where the structures or components are desired to be softerand/or more ductile, heat treating at a temperature above there-crystallization temperature may be more preferred. Without limitingthe scope of the applicants' invention, it is believed that the increasein adhesion strength and possible increase in intra-layer cohesion mayresult from a phenomenon known as diffusion bonding which results in thetransport of atoms across boundaries regions. It is also possible thatanother mechanism is, at least in part, responsible for the improvementin adhesion strength. This other mechanism may involve the reduction ofmetallic oxides that may exist at the interface between layers or atother locations within a structure.

In some alternative embodiments, it may be possible to heat treat astructure to improve interlayer adhesion and then after release and heattreatment, it may be possible to deposit a relatively uniform coating ofmaterial over the surface of the structures (e.g. by electroplating orthe like) to improve the hardness and yield strength of the combinedstructures.

In other alternatives to the present embodiment, the forming gas mayinclude H₂ in the range of about 1% to 10% or even higher. In stillother embodiments the atmosphere may be substantially pure H₂, while inother embodiments other reducing gases or agents may be usable. In stillother embodiments the atmosphere may be an inert gas such as N₂ or Ar.In still further embodiments the structures may be heat treated in avacuum. When a gas is present during heat treatment, that gas may beheld at a pressure below one atmosphere, at substantially oneatmosphere, or at some elevated pressure. During heat treatment, gas maybe present in a stagnant mode or it may be made to flow around thestructure or structures (this may be implemented in the form of a fanthat directs the gas around the chamber or in the form of a continuousflushing of gas through the chamber. In some embodiments, it may bedesirable to locate a second structural material between adjacent layersof the first structural material. This intermediate material may have amelting temperature or a recrystallization temperature below that of thestructural material and may be used to enhance diffusion bonding.

In some embodiments more than one structural material may exist in thestructure or component, depending on the function of each material (e.g.to give strength, enhanced conductivity, or dielectric properties), itmay be desirable to perform the heat treatment or diffusion bonding at atemperature which is below the lower of the two or morere-crystallization temperatures or below some intermediatere-crystallization temperature, or below the highest of there-crystallization temperatures.

In some alternatives to the present embodiment, various techniques maybe combined with the techniques explicitly presented herein. Forexample, it may be acceptable or desirable to perform the heat treatmentoperation with the sacrificial material still in place. In still otheralternatives, heat treatment or diffusion bonding may be practiced on apartially released structure (i.e. a structure or component where somesacrificial material still remains). In some embodiments separatestructures may be deliberately decoupled by introducing gaps betweenthem so as to eliminate or minimize the propagation of stressesassociated with differing coefficients of thermal expansion. In stillother alternative embodiments, during heat treatment compressive,mechanical forces may be applied along a direction which isperpendicular to the plane of the layers.

In still other alternative embodiments heat treatment may be performedwith the structure immersed in a liquid or in an environment where gaspressure or hydro-static pressure is greater than 10 to 50 PSI. In stillother alternative embodiments heat treatment may be performed prior tothe completion of formation of a structure. For example, it may beperformed on a layer by layer basis or periodically after the formationof a desired number of layers.

FIG. 15 depicts a block diagram of a tenth embodiment of the inventionwhere the structure is heat treated after formation at a temperaturethat significantly enhances interlayer adhesion but does notsignificantly decrease the yield strength of the intra-layer material.This embodiment starts with element 272 which calls for formation of amulti-layer structure with layers that are adhered to one another. Afterformation of the structure this embodiment, proceeds to element 274which calls for a heat treatment of the structure using a temperatureand time that significantly enhances the interlayer adhesion but doesnot significantly decrease the yield strength of the intra-layermaterial.

FIG. 16 depicts a block diagram of an eleventh embodiment of theinvention. As with the other embodiments discussed so far, thisembodiment starts with the formation of a multi-layer 3-dimensionalstructure where adjacent layers are adhered to one another. Afterformation of the structure, the structure is heat treated using atemperature and time such that the structure behaves monolithically upto at least 50% of the yield strength of the intra-layer material. Inother words, interlayer adhesion does not fail at tension levels thatare below 50% of the yield strength (i.e. the strength at which elasticdeformation gives rise to plastic deformation). In some alternatives,the monolithic behavior extends through the full elastic deformationregion while in even further embodiments it may extend substantiallyinto the plastic deformation region.

FIG. 17 depicts a block diagram of an eleventh embodiment of theinvention. This embodiment begins with element 292 which calls for aformation of a multi-layer structure where adjacent layers are adheredto one another. After formation of the structure, the process proceedsto element 294 which calls for heat treating the structure using atemperature and time such that a structure behaves monolithically up toat least 50% of the ultimate tensile strength of the intra-layermaterial. In other words, interlayer adhesion doesn't fail untiltensional forces cause stress and strain in the interlayer region toexceed 50% of the ultimate tensile strength of the material forming theintra-layer portions of the structure. Ultimate tensile strength refersto the tensile stress, per unit of original surface area, at which abody will fracture, or continue to deform under a decreasing load. Whenintra-layer tensile strength or yield strength is referred to herein,applicants mean the tensile strength or yield strength, respectively,that a sample would have when it is formed as the material is formedthat make up the layers without the existence of inter-layer boundaries.

FIG. 18 depicts a block diagram of a thirteenth embodiment of theinvention. In this embodiment of the invention the process begins withthe formation of a multi-layer structure where adjacent layers areadhered to one another. After formation, the process moves forward toelement 304 which calls for the heat treatment of the structure withinan atmosphere that is either inert or contains a reducing agent. Inertatmospheres include such gaseous material as nitrogen (N₂), argon (Ar),neon (Ne), and krypton (Kr), and the like. Reducing agents includehydrogen gas (H₂), and the like, as well as gas mixtures that containthese agents such as forming gases. In some alternative embodiments, itmay be possible to perform heat treatments in gases or under sprays ofmaterials, for example, that are not inert or offer reducing propertiesbut instead are chemically reactive with the structural material ormaterials that make up the structures. Such materials may include, forexample, carbon containing compounds that may interact with the surfacesof the structures to yield new structural characteristics for thedevices.

FIG. 19 depicts a block diagram of a fourteenth embodiment of theinvention where the structure is heat treated such that all portions ofthe structure reach a substantially uniform temperature. In thisembodiment the process begins with element 312 which calls for theformation of a multi-layer structure with adjacent layers that areadhered to one another. After formation, the process proceeds to element314 which calls for heat treatment of a structure using a substantiallyuniform temperature. In other words, using a temperature that hassubstantially the same value in all portions of a structure. In theseembodiments, for the temperature to be considered substantially uniform,the temperature variation throughout all regions of interest in astructure, during heat treatment, is preferably less than about 25° C.,more preferably less than about 15° C., and most preferably less thanabout 5° C. Alternatively, the temperature variation across a structureis preferably less than about 10% of the target temperature in ° C.,more preferably less than about 5% and even more preferably less thanabout 1%. At dwell temperature, the temperature of the structure ispreferably controlled within less than about 10% of the target dwelltemperature in ° C., more preferably within 5%, and even more preferablywithin 1%.

FIG. 20 depicts a block diagram of a fifteenth embodiment of theinvention where the structure is heat treated such that localtemperature differences do not directly result from localizeddifferences in electrical conductivity (e.g. do not result fromvariations in ohmic heating at different locations within a structure).In this embodiment of the invention, the process begins with theformation of the multi-layer structure where adjacent layers are adheredto one another. After formation, the process moves forward to element324 which calls for the heat treatment of the structure in a manner suchthat local temperature differences do not directly result from localizeddifferences in electrical conductivity of the structural material. Inthis embodiment heating of the structure preferably occurs byconvective, conductive or radiative application of heat to the surfaceof the structure. In some alternative embodiments, heating may occur bypassing a current through the devices but temperature variations acrossdifferent regions of a structure that result from ohmic heating arepreferably less than about 25° C., more preferably less than about 15°C., and most preferably less than about 5° C.

FIG. 21 depicts a flowchart of a sixteenth embodiment where thestructure is partially formed, released from sacrificial material, thenheat treated, and then completed with or without refilling ofsacrificial material and with or without further heat treating. In thisembodiment of the invention, the process begins with formation of aportion of a multi-layer structure. After the portion of the multi-layerstructure is formed, the process moves forward to element 334 whichcalls for the release of the multi-layer structure from at least onesacrificial material that was used during its formation of the portionof the structure. After removal of the sacrificial material, the processmoves forward to element 336 which calls for heat treating thestructure, for example, to enhance interlayer adhesion or to enhanceadhesion to other elements which may be added to the structure. Afterheat treatment the process moves forward to element 338 which inquiresas to whether replacement of the sacrificial material is necessary inorder to complete formation of the structure. If the answer is “no” theprocess proceeds to element 340 which calls for completing formation ofthe structure after which the process moves forward to element 342 whichinquires as to whether additional heat treating is to be performed, ifthe answer is “no” the process moves forward to element 344 and ends. Ifthe answer to the inquiry of element 342 is “yes”, the process movesforward to element 346 which calls for the performance of further heattreating and then moves forward to element 344 and ends.

If the answer to the inquiry of element 338 was “yes”, the process movesforward to element 352 which calls for the deposition of sacrificialmaterial and the potential planarization of that material in preparationfor forming additional layers of the structure. From element 352, theprocess moves forward to element 354 which calls for the completion ofthe formation of the structure. After the structure is completed, theprocess moves forward to element 356 which inquires as to whether or notthe sacrificial material is to be removed prior to any further heattreatment. If the answer is “yes”, the process moves forward to element358 which calls for the release of the completed structure from thesacrificial material after which the process moves to element 342 (whichwas discussed above) and either moves immediately to the end of theprocess at element 344 or proceeds to the heating treating called for byelement 346 and then ends at element 344.

If the answer to the inquiry of element 356 is “no” the process movesforward to element 360 which calls for the performance of additionalheat treatment after which the process moves forward to element 362which calls for the release of the completed structure from thesacrificial material. Thereafter, the process moves on to element 344and ends. This embodiment represents one of many possible combinationsof the previously discussed embodiments and is intended to be an exampleof how such combinations may be made. Alternative embodiments may allowmore than two releases of the partially formed structures and more thantwo heat treatments.

A seventeenth embodiment of the invention provides a low temperatureprocess for heat treating a structure that has been electrochemicallyfabricated (e.g. a nickel structure). The process leads to improvedinterlayer adhesion with less loss of mechanical strength than thatwhich may result from higher temperature processing. The primaryoperations of the process include:

-   -   1. Clean all released structures (i.e. structures which have        been separated from the sacrificial material used during their        formation) to remove organics and oxides by using a solvent and        dilute acid rinses    -   2. Place the structures in an environmental chamber that        provides for controlled temperature and atmosphere surrounding        the structures.    -   3. Replace the chamber atmosphere with forming gas (e.g. having        5% hydrogen and 95% nitrogen).    -   4. Close all openings to the chamber and maintain a positive        pressure of forming gas inside the chamber.    -   5. Ramp the temperature in the chamber from room temperature to        250° C. at a ramp rate of 10 degrees/minute. Monitor actual        chamber temperature so that it does not exceed the current        setpoint temperature by more than about 5° C. during at each        time interval and particularly during the dwell period at        maximum temperature. Keep a flow of forming gas going into the        chamber throughout the ramp up and dwell periods    -   6. Hold the temperature the dwell temperature (i.e. maximum        temperature) for 30 minutes (i.e. a dwell time)    -   7. Once dwell time ends, step down chamber temperature to room        temperature by allowing chamber to cool naturally and while        continuing the flow of forming gas for the first 30 minutes of        cool down period. After 30 minutes, the temperature should be        below 200° C. and the forming gas flow may be shut off.    -   8. Allow cooling to continue for another 30 minutes at which        point the temperature should be around 160° C. or less.    -   9. At this point, open chamber door and allow for convection        cooling with the room air. Allow cooling to continue for another        30 minutes. After this time, the temperature should be below        1000 C.    -   10. Remove the structures from the chamber and cool the wafer or        individual dies (if already diced) on chill plate by placing the        sample on a metal and allowing the temperatures to equalize.

Experiments were performed using the process of embodiment seventeen.These experiments used a nickel structural material and producedsignificantly improved interlayer adhesion and less overall loss ofstrength of the heated structures (when compared to structures treatedat higher temperatures). Inter-layer bonding was enhanced so thatinterlayer adhesion did not fail during the elastic compressions of thestructures and higher overall strength was retained (i.e. higher forceneeded to yield a given deflection). Various alternatives to theseventeenth embodiment are possible. For example, a lower dwelltemperature may be possible (e.g. 200, 150, or even 100 degrees C.);longer or shorter ramp up times and associated rates are possible,variations in the cool down process are possible, use of different gasenvironments during heating or cool down are possible (nitrogen only,hydrogen only, other ratios of nitrogen and hydrogen, use of inert gasessuch as argon, and the like); heat treatment before or after dicing;heat treatment before or after release; heat treatment before or aftersubstrate swapping, and the like. It will be within the abilities ofthose of skill in art to perform basic experiments and to determineappropriate or even optimal parameters for heat treating various buildand sacrificial materials.

Those of skill in the art will understand how to combine the variouspreviously presented embodiments to form more elaborate and/oralternative embodiments. The combined embodiments may take a singleaspect from two embodiments and combine them into a single embodiment orthey may take various aspects from more than two embodiments and combinethem.

It will be understood by those of skill in the art or will be readilyascertainable by them that various additional operations may be added tothe processes set forth herein. For example, between performances of thevarious deposition operations, performance of any etching operations,and performance of various planarization operations cleaning operations,activation operations, and the like may be desirable.

The patent applications and patents set forth below are herebyincorporated by reference herein as if set forth in full. The teachingsin these incorporated applications can be combined with the teachings ofthe instant application in many ways: For example, enhanced methods ofproducing structures may be derived from some combinations of teachings,enhanced structures may be obtainable, enhanced apparatus may bederived, and the like. U.S. Pat. App No., Filing Date U.S. App Pub. No.,Pub Date Inventor, Title 10/677,556 - Oct. 1, 2003 Cohen, “MonolithicStructures Including Alignment and/or Retention Fixtures for AcceptingComponents” XX/XX,XXX - Apr. 21, 2004 Cohen, “Methods of ReducingInterlayer (Docket P-US084-A-MF) Discontinuities in ElectrochemicallyFabricated Three- Dimensional Structures” XX/XXX,XXX - May 7, 2004Lockard, “Methods for Electrochemically Fabricating (DocketP-US099-A-MF) Structures Using Adhered Masks, Incorporating DielectricSheets, and/or Seed layers That Are Partially Removed Via Planarization”10/271,574 - Oct. 15, 2002 Cohen, “Methods of and Apparatus for MakingHigh 2003-0127336A - Jul. 10, 2003 Aspect Ratio MicroelectromechanicalStructures” 10/697,597 - Dec. 20, 2002 Lockard, “EFAB Methods andApparatus Including Spray Metal or Powder Coating Processes”10/677,498 - Oct. 1, 2003 Cohen, “Multi-cell Masks and Methods andApparatus for Using Such Masks To Form Three-Dimensional Structures”10/724,513 - Nov. 26, 2003 Cohen, “Non-Conformable Masks and Methods andApparatus for Forming Three-Dimensional Structures” 10/607,931- Jun. 27,2003 Brown, “Miniature RF and Microwave Components and Methods forFabricating Such Components” 10/387,958 - Mar. 13, 2003 Cohen,“Electrochemical Fabrication Method and 2003-022168A - Dec. 4, 2003Application for Producing Three-Dimensional Structures Having ImprovedSurface Finish” 10/434,494 - May 7, 2003 Zhang, “Methods and Apparatusfor Monitoring 2004-0000489A - Jan. 1, 2004 Deposition Quality DuringConformable Contact Mask Plating Operations” 10/434,289 - May 7, 2003Zhang, “Conformable Contact Masking Methods and 20040065555A - Apr. 8,2004 Apparatus Utilizing In Situ Cathodic Activation of a Substrate”10/434,294 - May 7, 2003 Zhang, “Electrochemical Fabrication MethodsWith 2004-0065550A - Apr. 8, 2004 Enhanced Post Deposition ProcessingEnhanced Post Deposition Processing” 10/434,295 - May 7, 2003 Cohen,“Method of and Apparatus for Forming Three- 2004-0004001A - Jan. 8, 2004Dimensional Structures Integral With Semiconductor Based Circuitry”10/434,315 - May 7, 2003 Bang, “Methods of and Apparatus for Molding2003-0234179A - Dec. 25, 2003 Structures Using Sacrificial MetalPatterns” XX/XXX,XXX - May 7, 2004 Thompson, “ElectrochemicallyFabricated Structures (Docket P-US104-A-MF) Having Dielectric or ActiveBases and Methods of and Apparatus for Producing Such Structures”10/724,515 - Nov. 26, 2003 Cohen, “Method for Electrochemically FormingStructures Including Non-Parallel Mating of Contact Masks andSubstrates” XX/XXX,XXX - May 7, 2004 Cohen, “Multi-step Release Methodfor (Docket P-US105-A-MF) Electrochemically Fabricated Structures”60/533,947 - Dec. 31, 2003 Kumar, “Probe Arrays and Method for Making”

Various other embodiments exist. Some of these embodiments may be basedon a combination of the teachings herein with various teachingsincorporated herein by reference. Some embodiments may not use anyblanket deposition process and/or they may not use a planarizationprocess. Some embodiments may use selective or blanket depositionsprocesses that are not electrodeposition processes. Some embodiments mayuse one or more structural materials (e.g. nickel, gold, copper, silver,or the like). Some processes may use one or more sacrificial materials(e.g. copper, silver, tin, zinc, or the like). Some embodiments mayremove a sacrificial material while other embodiments may not.

In view of the teachings herein, many further embodiments, alternativesin design and uses are possible and will be apparent to those of skillin the art. As such, it is not intended that the invention be limited tothe particular illustrative embodiments, alternatives, and usesdescribed above but instead that it be solely limited by the claimspresented hereafter.

1. A fabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer of material to apreviously formed layer and/or to a substrate, wherein the layercomprises a desired pattern of at least one material; and (b) repeatingthe forming and adhering operation of (a) at least twice to build up athree-dimensional structure from a plurality of adhered layers, whereinthe desired patterning on at least two layers is different; (c) afterformation of at least a plurality of layers, subjecting the multi-layerstructure to a heat treatment; wherein the structure comprises at leastone metal, and wherein formation of the desired pattern for at least onelayer comprises use of an adhered mask.
 2. The process of claim 1wherein the forming and adhering for at least two layers compriseselectrodepositing the at least one metal.
 3. The process of claim 2wherein the heat treatment results in improvement of adhesion strengthbetween metal deposits.
 4. The process of claim 1 wherein theelectrodepositing comprises electroplating the at least one metal. 5.The process of claim 4 wherein the heat treatment results in improvementof adhesion strength between metal deposits.
 6. The process of claim 2wherein the at least one metal comprises nickel.
 7. The process of claim1 wherein each of a plurality of layers comprises at least two metals,wherein at least one of the metals is a sacrificial material and atleast one other metal is a structural material that forms at least partof the structure.
 8. The process of claim 7 wherein the sacrificialmaterial comprises copper.
 9. The process of claim 7 wherein thestructural material comprises nickel.
 10. The process of claim 3 whereinthe adhesion strength increases by at least a factor of about two. 11.The process of claim 10 wherein the adhesion strength increases by atleast a factor of about five.
 12. The process of claim 1 wherein theheat treatment comprises heating the structure at more than about 250°C. for at least one hour.
 13. The process of claim 12 wherein the heattreatment comprises heating of the structure to more than about 250° C.for at least three hours.
 14. The process of claim 1 wherein the heattreatment comprises heating the structure at more than 200° C. for nomore than two hours.
 15. The process of claim 14 wherein an atmospherecomprising a reducing gas is located around the structure while atemperature of the structure is greater than about 200° C.
 16. Theprocess of claim 14 wherein an atmosphere comprising a reducing gas islocated around the structure while a temperature of the structure isgreater than about 100° C.
 17. The process of claim 1 wherein the heattreatment comprises heating the structure at more than 200° C. for nomore than one hour.
 18. The process of claim 17 wherein an atmospherecomprising a reducing gas is located around the structure while atemperature of the structure is greater than about 200° C.
 19. Theprocess of claim 17 wherein an atmosphere comprising a reducing gas islocated around the structure while a temperature of the structure isgreater than about 100° C.
 20. The process of claim 1 where theimprovement in adhesion strength results at least in part fromheat-aided material diffusion across a boundary where a later depositionjoins a surface of a previously deposited material.
 21. The process ofclaim 1 wherein the formation of a layer additionally comprises theplanarization of deposited material.
 22. The process of claim 7 whereinthe heat treatment occurs prior to a release of the sacrificial materialfrom the structural material.
 23. The process of claim 1 wherein theformation of at least a plurality of layers, comprises beginning adeposition operation to form a portion of a subsequent layer prior tocompleting formation of a previous layer.
 24. A process for forming amulti-layer three-dimensional structure, comprising: (a) forming apatterned deposit of at least one first material on to a substrate orpreviously deposited material such that at least one void exists aroundor within the patterned deposit of the at least first material; (b)depositing at least one second material into at least a portion of theat least one void; (c) trimming the deposit of at least on of the atleast one first material or the at least one second material to adesired level; (d) repeating the forming and adhering operations of(a)-(c) a plurality of times to build up a three-dimensional structurefrom a plurality of adhered layers; (e) after formation of at least aplurality of layers, subjecting the multi-layer structure to heattreatment, wherein at least one deposited material comprises a metal,and wherein the formaitng of the patterned deposit for at least onelayer comprises use of an adhered mask.
 25. The process of claim 24wherein the heat treatment results in an increase in the adhesionbetween at least a portion of the overlaying depositions of at least oneof the first and/or at least one of the second deposited materials. 26.The process of claim 25 wherein the enhanced adhesion results, at leastin part, from heat-aided diffusion of material across a boundary joiningtwo deposits.
 27. The process of claim 1 wherein the heat treatmentoccurs with a ratio of pressure along an axis perpendicular to a planeof the layers to that exerted along an axis parallel to the planes ofthe layers which is no greater than about
 10. 28. The process of 27wherein the ratio is no greater than about
 2. 29. The process of claim28 wherein the ratio is substantially
 1. 30. A fabrication process forforming a multi-layer three-dimensional structure, comprising: (a)forming and adhering a layer to a previously formed layer and/or to asubstrate; and (b) repeating the forming and adhering operation of (a)at least once to build up a three-dimensional structure from a pluralityof adhered layers, wherein at least a plurality of the layers eachcomprise at least two deposited materials; (c) after formation of atleast a plurality of layers and while at least two materials remain incontact adhered to one another, subjecting the multi-layer structure toa heat treatment; wherein the structure comprises at least one metal.31. A fabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer to a previouslyformed layer and/or to a substrate; and (b) repeating the forming andadhering operation of (a) at least once to build up a three-dimensionalstructure from a plurality of adhered layers, wherein the forming of atleast a plurality of layers comprises removing at least some depositedmaterial in a planarization operation; (c) after formation of at least aplurality of layers, subjecting the multi-layer structure to a heattreatment; wherein the structure comprises at least one metal, andwherein the forming and adhering of at least one layer comprises use ofan adhered mask in the selective patterning of at least one material.32. A fabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer to a previouslyformed layer and/or to a substrate, wherein the layer comprises adesired pattern of at least one material; and (b) repeating the formingand adhering operation of (a) at least once to build up athree-dimensional structure from a plurality of adhered layers, whereinthe desired patterning of at least one material deposited on asubsequent layer adheres directly to the desired patterning of at leastone material deposited on a preceding layer; (c) after formation of atleast a plurality of layers, subjecting the multi-layer structure to aheat treatment; wherein the structure comprises at least one metal, andwherein the forming and adhering of at least one layer comprises use ofan adhered mask in the selective patterning of at least one material.33. A fabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer to a previouslyformed layer and/or to a substrate, wherein the layer comprises adesired pattern of at least one material; and (b) repeating the formingand adhering operation of (a) at least once to build up athree-dimensional structure from a plurality of adhered layers; (c)after formation of at least a plurality of layers, subjecting themulti-layer structure to a heat treatment, wherein the structure isheated in a manner such that any local temperature variations within thestructure do not directly result from localized differences inelectrical conductivity of the structural material; wherein thestructure comprises at least one metal, and wherein the forming andadhering of at least one layer comprises use of an adhered mask in theselective patterning of at least one material.
 34. A fabrication processfor forming a multi-layer three-dimensional structure, comprising: (a)forming and adhering a layer to a previously formed layer and/or to asubstrate, wherein the layer comprises a desired pattern of at least onematerial; and (b) repeating the forming and adhering operation of (a) atleast once to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment such thatsubstantially all portions of the structure are heated to asubstantially uniform temperature; wherein the structure comprises atleast one metal.
 35. A fabrication process for forming a multi-layerthree-dimensional structure, comprising: (a) forming and adhering alayer to a previously formed layer and/or to a substrate, wherein thelayer comprises a desired pattern of at least one material; and (b)repeating the forming and adhering operation of (a) at least once tobuild up a three-dimensional structure from a plurality of adheredlayers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein amaximum temperature during heat treatment is less than arecrystallization temperature of at least one metal forming part of thestructure, and wherein the forming and adhering of at least one layercomprises use of an adhered mask in the selective patterning of at leastone material.
 36. A fabrication process for forming a multi-layerthree-dimensional structure, comprising: (a) forming and adhering alayer to a previously formed layer and/or to a substrate, wherein thelayer comprises a desired pattern of at least one material; and (b)repeating the forming and adhering operation of (a) at least once tobuild up a three-dimensional structure from a plurality of adheredlayers, wherein at least a plurality of the layers each comprise atleast one structural material and at least one sacrificial material; (c)separating the sacrificial material from the structure to release thestructure; and (d) after formation of at least a plurality of layers butprior to release, subjecting the multi-layer structure to a heattreatment; wherein the structure comprises at least one metal, andwherein the forming and adhering of at least one layer comprises use ofan adhered mask in the selective patterning of at least one material.37. A fabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer to a previouslyformed layer and/or to a substrate, wherein the layer comprises adesired pattern of at least one material; and (b) repeating the formingand adhering operation of (a) at least once to build up athree-dimensional structure from a plurality of adhered layers, whereinat least a plurality of the layers each comprise at least one structuralmaterial and at least one sacrificial material, and wherein the desiredpatterning on at least two layers is different; (c) separating thesacrificial material from the structure to release the structure; and(d) after release, subjecting the multi-layer structure to a heattreatment; wherein the structure comprises at least one metal, andwherein the forming and adhering of at least one layer comprises use ofan adhered mask in the selective patterning of at least one material.38. A fabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer to a previouslyformed layer and/or to a substrate, wherein the layer comprises adesired pattern of at least one material; and (b) repeating the formingand adhering operation of (a) at least once to build up athree-dimensional structure from a plurality of adhered layers; (c)subjecting the multi-layer structure to a heat treatment while thestructure is located in a selected atmosphere comprising an inert gas,wherein the structure comprises at least one metal.
 39. A fabricationprocess for forming a multi-layer three-dimensional structure,comprising: (a) forming and adhering a layer to a previously formedlayer and/or to a substrate, wherein the layer comprises a desiredpattern of at least one material; and (b) repeating the forming andadhering operation of (a) at least once to build up a three-dimensionalstructure from a plurality of adhered layers; (c) subjecting themulti-layer structure to a heat treatment while the structure is locatedin a selected atmosphere comprising a reducing gas, wherein thestructure comprises at least one metal.
 40. A fabrication process forforming a multi-layer three-dimensional structure, comprising: (a)forming and adhering a layer to a previously formed layer and/or to asubstrate, wherein the layer comprises a desired pattern of at least onematerial; and (b) repeating the forming and adhering operation of (a) atleast once to build up a three-dimensional structure from a plurality ofadhered layers, wherein at least a plurality of the layers each compriseat least one structural material and at least one sacrificial material,and wherein the desired patterning on at least two layers is different;(c) separating the sacrificial material from the structure to releasethe structure; (d) after release, subjecting the multi-layer structureto a heat treatment; (e) after the heat treatment, applying a secondsacrificial material to the structure. wherein the structure comprisesat least one metal.
 41. The fabrication process of claim 40 the secondsacrificial material comprises a material that is different from the atleast one sacrificial material which comprised a portion of the layers.42. The fabrication process of claim 40 the second sacrificial materialcomprises at least one material that is substantially the same as the atleast one sacrificial material which comprised a portion of the layers.43. The fabrication process of claim 40 the second sacrificial materialis removed.
 44. A fabrication process for forming a multi-layerthree-dimensional structure, comprising: (a) forming and adhering alayer of material to a previously formed layer and/or to a substrate,wherein the layer comprises a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leasttwice to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment; and (d)releasing the structure from the substrate, wherein the structurecomprises at least one metal, and wherein the forming and adhering of atleast one layer comprises use of an adhered mask in the selectivepatterning of at least one material.
 45. The fabrication process ofclaim 44 wherein the structure is released from the substrate prior toheat treatment.
 46. The fabrication process of claim 44 wherein thestructure is released from the substrate after heat treatment.
 47. Afabrication process for forming a multiple multi-layer three-dimensionalstructures, comprising: (a) forming and adhering a layer of material toa previously formed layer and/or to a substrate, wherein the layercomprises a desired pattern of at least one material; and (b) repeatingthe forming and adhering operation of (a) at least twice to build up aplurality of three-dimensional structures from a plurality of adheredlayers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment; and (d) dicingthe plurality of structures from one another, wherein the structurecomprises at least one metal.
 48. The fabrication process of claim 47wherein the dicing occurs in at least two steps, one of which results inpartial dicing prior to heat treatment, and another of which results inthe completion of dicing after heat treatment.
 49. The fabricationprocess of claim 47 wherein the dicing is completed prior to heattreatment.
 50. The fabrication process of claim 47 wherein the dicing iscompleted after heat treatment.
 51. A fabrication process for forming amulti-layer three-dimensional structure, comprising: (a) forming andadhering a layer to a previously formed layer and/or to a substrate,wherein the layer comprises a desired pattern of at least one material;and (b) repeating the forming and adhering operation of (a) at leastonce to build up a three-dimensional structure from a plurality ofadhered layers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein amaximum effective temperature during heat treatment is less than arecrystallization temperature of at least one metal forming part of thestructure, and wherein the heat treatment is applied for a sufficienttime and at a sufficient temperature and in an environment that allowsinterlayer adhesion to be enhanced a substantial amount, and wherein theforming and adhering of at least one layer comprises use of an adheredmask in the selective patterning of at least one material.
 52. Theprocess of claim 51 wherein the substantial amount comprises at least afactor of two.
 53. The process of claim 51 wherein the substantialamount comprises at least a factor of five.
 54. The process of claim 51wherein the substantial amount corresponds to the interlayer adhesionstrength being greater than about 50% of the yield strength of theinterlayer material.
 55. The process of claim 51 wherein the substantialamount corresponds to the interlayer adhesion strength being greaterthan about the yield strength of the interlayer material.
 56. Theprocess of claim 51 wherein the substantial amount corresponds to theinterlayer adhesion strength being greater than about 50% of theultimate tensile strength of the intra-layer material.
 57. A fabricationprocess for forming a multi-layer three-dimensional structure,comprising: (a) forming and adhering a layer to a previously formedlayer and/or to a substrate, wherein the layer comprises a desiredpattern of at least one material; and (b) repeating the forming andadhering operation of (a) at least once to build up a three-dimensionalstructure from a plurality of adhered layers; (c) after formation of atleast a plurality of layers, subjecting the multi-layer structure to aheat treatment, wherein the heat treatment is applied to the structurefor a temperature, a time, and in an environment such that a substantialincrease in interlayer adhesion results without significantly reducingthe yield strength of the intra-layer material, and wherein the formingand adhering of at least one layer comprises use of an adhered mask inthe selective patterning of at least one material.
 58. The process ofclaim 57 wherein the substantial increase comprises at least a factor oftwo and the reducing is no more than 50% of the yield strength prior toheat treatment.
 59. The process of claim 57 wherein the substantialamount comprises at least a factor of five and the reducing is no morethan 75% of the yield strength prior to heat treatment.
 60. The processof claim 57 wherein the substantial amount corresponds to the interlayeradhesion strength being greater than about 50% of the yield strengthprior to heat treatment and the yield strength after heat treatment isno less than 75% of the yield strength prior to heat treatment.
 61. Theprocess of claim 57 wherein the substantial amount corresponds to theinterlayer adhesion strength being greater than about the yield strengthafter heat treatment and the yield strength after heat treatment beingno less than 75% of its value prior to heat treatment.
 62. The processof claim 57 wherein the substantial amount corresponds to the interlayeradhesion strength being greater than about 50% of the ultimate tensilestrength of the intra-layer material and the ultimate tensile strengthof the interlayer material being no less than 75% of its value prior toheat treatment.
 63. A fabrication process for forming a multi-layerthree-dimensional structure, comprising: (a) forming and adhering alayer to a previously formed layer and/or to a substrate, wherein thelayer comprises a desired pattern of at least one material; and (b)repeating the forming and adhering operation of (a) at least once tobuild up a three-dimensional structure from a plurality of adheredlayers; (c) after formation of at least a plurality of layers,subjecting the multi-layer structure to a heat treatment, wherein theheat treatment results in the formation of a structure which behavesmonolithically up to at least 50% of the yield strength of theintra-layer material, and wherein the forming and adhering of at leastone layer comprises use of an adhered mask in the selective patterningof at least one material.
 64. The process of claim 63 wherein yieldstrength of the intra-layer material is that of the intra-layer materialprior to heat treatment.
 65. The process of claim 63 wherein yieldstrength of the intra-layer material is that of the intra-layer materialafter heat treatment.
 66. The process of claim 63 wherein monolithicbehavior exists when stresses are at or below 50% of the yield strengthof the intra-layer material and inter-layer adhesion failure is no morelikely to occur than intra-layer cohesion failure.
 67. The process ofclaim 63 wherein monolithic behavior exists when stresses are at orbelow about 50% of the ultimate yield strength of the intra-layer. 68.The process of claim 67 wherein yield strength of the intra-layermaterial is that of the intra-layer material prior to heat treatment.69. The process of claim 67 wherein yield strength of the intra-layermaterial is that of the intra-layer material after heat treatment.
 70. Afabrication process for forming a multi-layer three-dimensionalstructure, comprising: (a) forming and adhering a layer to a previouslyformed layer and/or to a substrate, wherein the layer comprises adesired pattern of at least one material; and (b) repeating the formingand adhering operation of (a) at least once to build up athree-dimensional structure from a plurality of adhered layers; (c)after formation of at least a plurality of layers, subjecting themulti-layer structure to a heat treatment, wherein the heat treatmentresults in the formation of a structure which is no more likely toexperience interlayer adhesion failure than intra-layer cohesion failurewhen applied stress is at least 50% of the yield strength of theintra-layer material.
 71. The process of claim 70 wherein yield strengthof the intra-layer material is that of the intra-layer material prior toheat treatment.
 72. The process of claim 70 wherein yield strength ofthe intra-layer material is that of the intra-layer material after heattreatment.